48 ME. J. A. DOUGLAS ON GEOLOGICAL SECTIONS [April 1914, 



and basalts of Mount Tacora and Chupiquina. These and other 

 high volcanic peaks now constitute the Western Cordillera. To 

 the east of these growing cones appears to have existed an inland 

 sea or system of lakes, and the extensive deposits of the Mauri 

 Volcanic Series were probably laid down in great part below 

 water. The great lake-system, of which Lake Titicaca and Lake 

 Poopoo are remnants, was possibly cut off as an arm of the sea 

 during Miocene times, and gradually elevated to its present 

 position. The whole country lay at a considerably lower altitude 

 than it does at present, and supported an abundant mammalian 

 fauna during Pleistocene times. The glaciers advanced down the 

 valleys during the Glacial Period, and retreated once more to the 

 mountain-tops, leaving behind them abundant proof of their former- 

 extension. 



The uplift continued even during the time of human existence ; 

 the rainfall from the east gradually became cut off; and the lake- 

 waters receded to their present limits. 



Now we find a vast, arid, high-level plateau, the Bolivian Alta- 

 planicie, almost devoid of vegetation and inhabited by a decadent 

 race of Indians where once thrived a highly-cultured civilization. 

 On the east it is cut off from the densely-forested region of the 

 Amazon basin by the inaccessible snow-peaks of the Eastern 

 Cordillera, formed of granite and Palaeozoic sediments ; on the 

 west from the coastal deserts of the Pacific Ocean by the giant 

 volcanic cones of the Western Cordillera. 



According to Mr. McCurdy, one of the oldest European resi- 

 dents of Arica, a slight recent elevation of the coast is suggested bv 

 the shallowing during the last twenty years of the rocky bathing- 

 ground, but that the movement has practically ceased is shown by 

 the presence of pre-Spanish Indian burial-tumuli only a few feet 

 above high- water level. 



In conclusion, I have to express my best thanks, not only to 

 Mr. W. E. Balston, who enabled me to undertake the work, but 

 also to many friends who gave me assistance during my stay in the 

 country ; to Mr. Wynne Edwards, Sir John Jackson's repre- 

 sentative in Chile, in charge of the construction of the Arica— 

 La Paz Railway, and his assistant engineers, Mr. Clark, Mr. 

 McDonald, and many others for their kind hospitality; also to 

 Mr. Henry Schumacher, of Tacna, to whom I owe a deep debt 

 of gratitude for placing his extensive knowledge of the country at 

 my disposal ; and, finally, to Senor Escutti Orrego, of Arica, and 

 to Senor Don Manuel V. Ballivian, of La Paz, who gave us 

 letters of introduction throughout Bolivia. 



I also take this opportunity of acknowledging the kind help 

 and advice which I have received from the following geologists 

 during the working out of my results : — Dr. C. W. Andrews, 

 Miss N. Bancroft, Dr. F. A. Bather, Dr. J. S. Flett, Mr. R. 

 B. Newton, Prof. W. J. Sollas, Dr. A. Vaughan, and Dr. A. Smith 

 Woodward. 



